The use of optical fibers as a medium for transmission of digital data (including voice, interne and IP video data) is becoming increasingly more common due to the high reliability and large bandwidth available with optical transmission systems. Fundamental to these systems are optical subassemblies for transmitting and/or receiving optical signals.
A common optical subassembly comprises an interposer. As used herein, an interposer functions as a substrate for optical, opto-electrical, and electrical components and provides interconnections to optically and/or electrically interconnect the optical/opto-electrical/electrical components. For example, a typical interposer may comprise a substrate comprising, for example, silicon, having one or more grooves formed therein for holding fibers precisely. A conventional groove is formed in the shape of a “V” by wet etching the substrate to include two sidewalls that retain the optical fiber along its length. Wet etching a crystalline material such as silicon results in a predictable and very precise etch along the crystalline plane of the material. For example, silicon has a crystalline plane of 54.7°, thus, the sidewalls and the end face are typically formed at a precise angle of 54.7° from the reference surface.
The end face of a conventional interposer V-groove is metalized so that it may be used as a mirror to reflect light between the optical/opto-electrical component and the optical fiber. For example, in the case of a transmitter, an opto-electrical light source emits a cone-shaped light beam onto the V-groove end face mirror. The V-groove end face mirror reflects the light through an end of the optical fiber retained in the V-groove. As discussed above, the surface of the V-groove end face is at an angle of precisely 54.7° from the reference surface. As such, light is reflected off the groove end face mirror through the optical fiber at approximately −9.3° from the reference surface and also from the longitudinal axis of the optical fiber retained in the V-groove. Therefore, current devices utilizing the end face mirror of the groove to launch light through an end of the optical fiber cause much of the light to be reflected away from the axis of the optical fiber resulting in non-optimal signal transmission performance.
Applicants recognize that there is a need for an improved optical coupling between the optical device and the optical conduit. Additionally, Applicants recognize that this optical coupling should be achievable through passive alignment rather than active alignment to facilitate economic production of the subassembly. To this end, a patent application (U.S. application Ser. No. 12/510,954, incorporated herein referenced) was filed recently, which discloses a multi-faceted fiber end face mirror for optical coupling. Specifically, the facets of the fiber end face mirror included a 54.7° facet to mechanically contact the end face of the V-groove to precisely position the optical fiber end face mirror in the V-groove along the longitudinal axis and under the emission aperture of the opto-electrical device. Additionally, another facet was a 45° facet to facilitate optimal optical coupling between the optical axis of the fiber and the optical axis of the opto-electrical device. Additional facets were also disclosed for enhancing performance. Each of these facets would then be coated with a metal to act as a reflective mirror surface.
Although this development improved the optical performance and facilitated passive alignment of the subassembly, it also required coating the fiber end face on a number of different facets with a metallic/reflective coating. Applicants have identified an additional need to avoid the requirement for depositing a reflecting coating on fiber end faces as such a process tends to be complicated and expensive, and does not lend itself to a high-volume manufacturing.
Therefore, a need exists for a simplified approach for preparing an optical subassembly having a 90° optical coupling that can be prepared using high-volume, economical manufacturing techniques. The present invention fulfills this need among others.